1. Field of the Invention
The present invention relates to a trench etching process. More particularly, it relates to a trench etching process wherein a completion of a required etching process in a trench can be determined by detecting a change in emission analysis results.
2. Description of the Related Art
With the enhancement of the degree of integration of IC's, the trench etching process for, for example, silicon, has become extremely important when miniaturizing the area of the isolation and capacitor cells.
In a trench etching process for producing a trench in a silicon substrate, a precise and reproducible control of the depth of the trench is difficult, since there is no layer which can act as a stopper layer, and accordingly, there is no known effective means for controlling the distribution of the respective depths of trenches over the entire surface of the silicon substrate.
A conventional trench etching process is shown in FIGS. 1A to 1C. As shown in FIG. 1A, a phosphosilicate glass (PSG) layer 2 having a thickness of, for example, 1.0 .mu.m is formed on a silicon substrate 1. As shown in FIG. 1B, an opening 3 by which the silicon substrate 1 is exposed is formed in the PSG layer 2 in which a trench is to be formed, by photolithography. After forming the opening 3, as shown in FIG. 1C, a trench 4 is formed in the silicon substrate 1 by a reactive ion etching (RIE) process using the remaining PSG layer 2 as a mask.
The RIE process for producing a required trench is usually carried out by a time control. Namely, the time is predetermined by calculating the RIE etching rate of the silicon substrate. Further, the RIE process for producing the required trench is usually carried out while monitoring the depth of the trench by calculating a difference between the time when laser beam is reflected from the surface of the silicon substrate and from the bottom surface of the trench.
Such a conventional trench etching process, wherein a time control is carried out, is disadvantageous in that there is no guarantee that a required etching has been carried out, since no warning is given if a required etching is not realized due to unforeseen circumstances. Further, when the depth of trench is monitored by using a laser beam, etc., the monitoring precision is reduced due to the shape of the trench.
Japanese Unexamined Patent Publication (Kokai) No. 61-232620, published on Oct. 16, 1986, discloses a process for etching a semiconductor substrate wherein an etching end point is detected by monitoring the emission intensity of an atom or molecule or an ion of components of an etching mask. In this etching process, the completion of a trench etching can be precisely and reproducibly detected, but when many trenches having the same depth are formed in a silicon substrate, a uniform distribution of the depth of the trenches can not be obtained over an entire surface of the silicon substrate, since the etching mask is not directly laid on the silicon substrate and the etching rate of a film disposed between the etching mask and the silicon substrate is not the same as that of the silicon substrate.